Optically anisotropic sheet comprising aligned discotic liquid crystal molecules

ABSTRACT

An optically anisotropic sheet comprises an optically anisotropic layer, an orientation layer and a transparent support in this order. The optically anisotropic layer is formed from discotic liquid crystal molecules. The orientation layer is subjected to rubbing treatment. The discotic liquid crystal molecules are aligned with the orientation layer. An average inclined angle of discotic planes of the discotic liquid crystal molecules is in the range of 50° to 90°. An average direction of optical axes of the discotic liquid crystal molecules is essentially parallel to a rubbing direction of the orientation layer.

FIELD OF THE INVENTION

[0001] The present invention relates to an optically anisotropic sheetcomprising aligned discotic liquid crystal molecules. The invention alsorelates to a polarizing plate comprising an optically anisotropic layer,an orientation layer, a transparent support, a polarizing film and atransparent protective film in this order. The invention further relatesto a process for orienting discotic liquid crystal molecules with anorientation layer.

BACKGROUND OF THE INVENTION

[0002] A liquid crystal display comprises a liquid crystal cell, apolarizing element and an optical compensatory sheet (phase retarder).In a liquid crystal display of transmission type, two polarizingelements are arranged on both-sides of the liquid crystal cell and oneor two optical compensatory sheets (phase retarders) are arrangedbetween the liquid crystal cell and the polarizing elements. On theother hand, a liquid crystal display of reflection type comprises areflection plate, a liquid crystal cell, an optical compensatory sheetand a polarizing element in this order.

[0003] The liquid crystal cell comprises a pair of substrates, rod-likeliquid crystal molecules and an electrode layer. The rod-like liquidcrystal molecules are provided between the substrates. The electrodelayer has a function of applying a voltage to the rod-like liquidcrystal molecules. Each of the substrates has an orientation layer,which has a function of aligning the rod-like liquid crystal molecules.The alignment of the rod-like liquid crystal molecules is determinedaccording to a display mode of the liquid crystal cell. Various displaymodes of the liquid crystal cell have been proposed. Examples of themode for transmission type include TN (Twisted Nematic) mode, IPS(In-Plane Switching) mode. FLC (Ferroelectric Liquid Crystal) mode, OCB(Optically Compensatory Bend) mode, STN (Super Twisted Nematic) mode, VA(Vertically Aligned) mode and ECB (Electrically ControlledBirefringence) mode. Examples of the mode for reflection type include TNmode, HAN (Hybrid Aligned Nematic) mode and GH (Guest-Host) mode.

[0004] The optical compensatory sheet has functions of removingundesired color from a displayed image and enlarging a viewing angle. Asthe optical compensatory sheet, a stretched birefringent film has beenconventionally used.

[0005] Recently, an optical compensatory sheet comprising an opticallyanisotropic layer on a transparent support has been proposed in place ofthe stretched birefringent film. The optically anisotropic layer isformed from liquid crystal molecules. Since the liquid crystal moleculeshave various alignment forms, an optical compensatory sheet obtained byusing the liquid crystal molecules has specific optical characteristicsthat cannot be obtained by the conventional stretched birefringent film.

[0006] The optical characteristics of the optical compensatory sheet aredetermined according to optical characteristics (i.e., display mode) ofthe liquid crystal cell. Various optical compensatory sheets properlyapplied for various display modes can be produced by using liquidcrystal molecules. As the liquid crystal molecules for opticalcompensatory sheet, rod-like or discotic liquid crystal molecules aregenerally used.

[0007] Various optical compensatory sheets using discotic liquid crystalmolecules according to various display modes have been disclosed. Forexample, an optical compensatory sheet for TN mode is disclosed inJapanese Patent Provisional Publication No. 6(1994)-214116, U.S. Pat.Nos. 5,583,679, 5,646,703 and German Patent Publication No. 3,911,620A1.An optical compensatory sheet for IPS or FLC mode is disclosed inJapanese Patent Provisional Publication No. 10(1998)-54982, and a sheetfor OCB or HAN mode is disclosed in U.S. Pat. No. 5,805,253 andInternational Patent No. WO96/37804. Further, a compensatory sheet forSTN mode is disclosed in Japanese Patent Provisional Publication No.9(1997)-26572, and one for VA mode is disclosed in Japanese Patent No.2,866,372.

[0008] In the optical compensatory-sheet for STN mode disclosed inJapanese Patent Provisional Publication No. 9(1997)-26572, the discoticliquid crystal molecules are aligned at an average inclined angle of 50°to 90° (namely, the liquid crystal molecules are vertically aligned).

SUMMERY OF THE INVENTION

[0009] An optically anisotropic sheet comprises discotic liquid crystalmolecules aligned at an average inclined angle of 50° to 90°. In theoptically anisotropic sheet, an average direction of optical axes(normal lines to the discotic planes) of the molecules is generallyperpendicular to a rubbing direction of the orientation layer. Theoptically anisotropic sheet is practically produced in the form of aroll. It is the easiest way to conduct a rubbing treatment along alongitudinal direction of the rolled sheet. Accordingly, the most easilyproduced optical compensatory sheet having an optically anisotropiclayer in which the discotic liquid crystal molecules are aligned at anaverage inclined angle of 50° to 90° has an average direction of opticalaxes perpendicular to the longitudinal direction (i.e., the averagedirection of optical axes is parallel to the lateral direction).

[0010] In a polarizing element having stretched polymer film, thetransparent axis is perpendicular to the stretching direction. Thepolarizing element is also practically produced in the form of a roll.It is the easiest way to stretch the film along the longitudinaldirection of the roll. Accordingly, the most easily produced polarizingelement has a transparent axis perpendicular to the longitudinaldirection (i.e., the transparent axis of that polarizing element isparallel to the lateral direction).

[0011] Where the rolled optically anisotropic sheet is laminated withthe rolled polarizing element, the optical axes of discotic liquidcrystal molecules and the transparent axis of the element are easily soarranged that the optical axes are essentially parallel to thetransparent axis.

[0012] However, the optical axes and the transparent axis of the elementare preferably so arranged in some display modes that the optical axesare essentially perpendicular to the transparent axis.

[0013] The discotic liquid crystal molecules must be so aligned that theoptical axes of liquid crystal molecules are parallel to the rubbingdirection of the orientation layer to arrange the optical axes along thelongitudinal direction of the rolled sheet. In the presentspecification, the words “the optical axes of discotic liquid crystalmolecules are parallel to the rubbing direction of the orientationlayer” mean that an average direction of lines obtained by projectingthe normal lines to the discotic planes of the molecules on the supportis parallel to the rubbing direction. A new orientation layer havingsuch function is required to orient the optical axes of the discoticliquid crystal molecules parallel to the rubbing direction. Aconventional orientation layer orients the optical axes of the discoticliquid crystal molecules perpendicularly to the rubbing direction.

[0014] An object of the present invention is to provide an opticallyanisotropic sheet in which discotic liquid crystal molecules are soaligned that the optical axes are parallel to the rubbing direction.

[0015] Another object of the invention is to provide a polarizing platein which the optical axes of discotic liquid crystal molecules areeasily arranged essentially perpendicularly to the transparent axis ofpolarizing film.

[0016] A further object of the present invention is to align discoticliquid crystal molecules so that the optical axes are parallel to therubbing direction.

[0017] The present invention provides an optically anisotropic sheetcomprising an optically anisotropic layer formed from discotic liquidcrystal molecules, an orientation layer subjected to rubbing treatmentand a transparent support in this order, wherein the discotic liquidcrystal molecules are so aligned that an average inclined angle ofdiscotic planes of the discotic liquid crystal molecules is in the rangeof 50° to 90° and that an average direction of optical axes of thediscotic liquid crystal molecules is essentially parallel to a rubbingdirection of the orientation layer.

[0018] The invention also provides a rolled polarizing plate comprisingan optically anisotropic layer formed from discotic liquid crystalmolecules, an orientation layer subjected to rubbing treatment, atransparent support, a polarizing film and a transparent protective filmin this order, wherein the discotic liquid crystal molecules are soaligned that an average inclined angle of discotic planes of thediscotic liquid crystal molecules is in the range of 50° to 90° and thatan average direction of optical axes of the discotic liquid crystalmolecules is essentially parallel to a rubbing direction of theorientation layer.

[0019] The invention further provides a process for orienting discoticliquid crystal molecules, comprising the steps of: coating a solution ofa copolymer comprising repeating units represented by the formula (I)and repeating units represented by the formula (II) on a support to forma coated layer; rubbing a surface of the coated layer to form anorientation layer; coating a solution containing discotic liquid crystalmolecules on the orientation layer to orient the discotic liquid crystalmolecules so that an average inclined angle of discotic planes of thediscotic liquid crystal molecules is in the range of 50° to 90° and thatan average direction of optical axes of the discotic liquid crystalmolecules is essentially parallel to a rubbing direction of theorientation layer:

[0020] in which each of R¹ and R² independently is hydrogen, a halogenatom or an alkyl group having 1 to 6 carbon atoms; M is an alkali metalion; L¹ is a divalent linking group selected from the group consistingof —O—, —CO—, —NH—, an alkylene group and a combination thereof; each ofL², L³ and L⁴ independently is a single bond or a divalent linking groupselected from the group consisting of —O—, —CO—, —NH, —SO₂—, an alkylenegroup, an alkenylene group, an alkynylene group and a combinationthereof; each of Ar¹, Ar², Ar³ and Ar⁴ independently is an aromaticring, which can have a substituent group; each of m and n independentlyis 0 or 1; x is 10 to 95 mole %; and y is 5 to 90 mole %.

[0021] In the present specification, the term “essentiallyperpendicular” or “essentially parallel” means that the angle betweenthe noticed directions is within the range of 90°±5° or 0°±5°,respectively. The allowance of the angle is preferably less than ±4°,more preferably less than ±3°, further preferably less than ±2°, andmost preferably less than ±1°.

[0022] The present inventors have succeeded in aligning discotic liquidcrystal molecules, whose optical axes are parallel to the rubbingdirection. In the prepared optically anisotropic sheet, discotic liquidcrystal molecules are so aligned that the optical axes are essentiallyparallel to the rubbing direction. A rolled optically anisotropic sheetcomprising discotic liquid crystal molecules whose optical axes areparallel to the longitudinal direction can be easily produced.

[0023] Further, a polarizing element having a transparent axisperpendicular to the longitudinal direction (i.e., along the lateraldirection) is most easily produced. Therefore, a polarizing plate inwhich the optical axes of discotic liquid crystal molecules areessentially perpendicular to the transparent axis of the polarizing filmcan be easily produced by simply laminating the rolled opticallyanisotropic sheet and the rolled polarizing element of the inventionwith their rolled forms maintained.

[0024] According to the invention, it is easy to arrange the opticalaxes of discotic liquid crystal molecules essentially perpendicularly tothe transparent axis of the polarizing film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 schematically illustrates basic structures of liquidcrystal displays of transmission type.

[0026]FIG. 2 schematically illustrates a basic structure of a liquidcrystal display of reflection type.

[0027]FIG. 3 schematically illustrates the step for laminating a rolledoptically anisotropic sheet and a rolled polarizing element.

[0028]FIG. 4 schematically illustrates alignment of discotic liquidcrystal molecules in the optically anisotropic sheet.

DETAILED DESCRIPTION OF THE INVENTION

[0029]FIG. 1 schematically illustrates basic structures of liquidcrystal displays of transmission type.

[0030] The liquid crystal display shown in FIG. 1(a) comprises abacklight (BL), a transparent protective film (1 a), a polarizing film(2 a), a transparent support (3 a), an optically anisotropic layer (4a), a lower substrate of liquid crystal cell (5 a), a layer of rod-likeliquid crystal molecules (6), an upper substrate of liquid crystal cell(5 b), an optically anisotropic layer (4 b), a transparent support (3b), a polarizing film (2 b) and a transparent protective film (1 b) inthis order.

[0031] Each combination of the transparent support and the opticallyanisotropic layer (each of 3 a-4 a and 4 b-3 b) constitutes an opticallyanisotropic sheet. Each combination of the transparent protective film,the polarizing film, the transparent support and the opticallyanisotropic layer (each of 1 a to 4 a and 4 b to 1 b) constitutes apolarizing plate.

[0032] The transparent supports (3 a, 3 b) have orientation layers onthe side facing the optically anisotropic layers. (4 a, 4 b), and thelower and upper substrates of liquid crystal cell (5 a, 5 b) also haveorientation layers on the side facing the layer of rod-like liquidcrystal molecules (6).

[0033] The liquid crystal display shown in FIG. 1(b) comprises abacklight (BL), a transparent protective film (1 a), a polarizing film(2 a), a transparent support (3 a), an optically anisotropic layer (4a), a lower substrate of liquid crystal cell (5 a), a layer of rod-likeliquid crystal molecules (6), an upper substrate of liquid crystal cell(5 b), a transparent protective film (1 b), a polarizing film (2 b) anda transparent protective film (1 c) in this order.

[0034] The combination of the transparent support and the opticallyanisotropic layer (3 a-4 a) constitutes an optically anisotropic sheet.The combination of the transparent protective film, the polarizing film,the transparent support and the optically anisotropic layer (1 a to 4 a)constitutes a polarizing plate.

[0035] The transparent support (3 a) has an orientation layer on theside facing the optically anisotropic layer (4 a), and the lower andupper substrates of liquid crystal cell (5 a, 5 b) also have orientationlayers on the side facing the layer of rod-like liquid crystal molecules(6).

[0036] The liquid crystal display shown in FIG. 1(c) comprises abacklight (BL), a transparent protective film (1 a), a polarizing film(2 a), a transparent protective film (1 b), a lower substrate of liquidcrystal cell (5 a), a layer of rod-like liquid crystal molecules (6), anupper substrate of liquid crystal cell (5 b), an optically anisotropiclayer (4 b), a transparent support (3 b), a polarizing film (2 b) and atransparent protective film (1 c) in this order.

[0037] The combination of the transparent support and the opticallyanisotropic layer (4 b-3 b) constitutes an optically anisotropic sheet.The combination of the transparent protective film, the polarizing film,the transparent support and the optically anisotropic layer (4 b to 1 c)constitutes a polarizing plate.

[0038] The transparent support (3 b) has an orientation layer on theside facing the optically anisotropic layer (4 b), and the lower andupper substrates of liquid crystal cell (5 a, 5 b) also have orientationlayers on the side facing the layer of rod-like liquid crystal molecules(6).

[0039]FIG. 2 schematically illustrates a basic structure of a liquidcrystal display of reflection type.

[0040] The liquid crystal display shown in FIG. 2 comprises a lowersubstrate of liquid crystal cell (5 a), a reflection plate (RP), a layerof rod-like liquid crystal molecules (6), an upper substrate of liquidcrystal cell (5 b), an optically anisotropic layer (4), a transparentsupport (3), a polarizing film (2) and a transparent protective film (1)in this order.

[0041] The combination of the transparent support and the opticallyanisotropic layer (4-3) constitutes an optically anisotropic sheet. Thecombination of the transparent protective film, the polarizing film, thetransparent support and the optically anisotropic layer (4 to 1)constitutes a polarizing plate.

[0042] The transparent support (3) has an orientation layer on the sidefacing the optically anisotropic layer (4). The reflection plate (RP)and the upper substrate of liquid crystal cell (5 b) also haveorientation layers on the side, facing the layer of rod-like liquidcrystal molecules (6).

[0043]FIG. 3 schematically illustrates the step for laminating a rolledoptically anisotropic sheet and a rolled polarizing element.

[0044] As shown in FIG. 3, the rolled polarizing element comprises atransparent protective film (1) and a polarizing film (2). The rolledoptically anisotropic sheet comprises a transparent support (3) and anoptically anisotropic layer (4), and the transparent support (3) has anorientation layer on the side facing the optically anisotropic layer(4).

[0045] The transparent axis (TA) of the polarizing film (2) isessentially perpendicular to the longitudinal direction (LD) of therolled polarizing element. The optical axes (OA) of discotic liquidcrystal molecules in the optically anisotropic layer (4) are essentiallyparallel to the longitudinal direction (LD) of the rolled opticallyanisotropic sheet. Consequently, the transparent axis (TA) of thepolarizing film (2) is easily arranged essentially perpendicularly tothe optical axes (OA) of discotic liquid crystal molecules in theoptically anisotropic layer (4) by simply laminating the rolledoptically anisotropic sheet and the rolled polarizing element as shownin FIG. 3.

[0046] In FIGS. 1 to 3, the transparent support (3) and the opticallyanisotropic layer (4) may be placed in reverse order.

[0047]FIG. 4 schematically illustrates alignment of discotic liquidcrystal molecules in the optically anisotropic sheet.

[0048] The optically anisotropic sheet shown in FIG. 4 comprises anoblong transparent support (3), an orientation layer (O) subjected torubbing treatment and an optically anisotropic layer (4) formed fromdiscotic liquid crystal molecules. The longitudinal direction (LD) ofthe support (3) is parallel to the rubbing direction (RD) of theorientation layer (O). The optical axes (OA) of discotic liquid crystalmolecules (DLC) are also parallel to the longitudinal direction (LD) ofthe support (3) and the rubbing direction (RD) of the orientation layer(O).

[0049] [Support]

[0050] The support is preferably transparent. A glass plate or a polymerfilm (preferably, a polymer film) can be used as the transparent supportof the optically anisotropic sheet. The term “transparent” means thatlight transmittance is not less than 80%.

[0051] An optically isotropic polymer film is generally used as thetransparent support. The retardation in plane (Re) of the support ispreferably less than 20 nm, more preferably less than 10 nm, and mostpreferably less than 5 nm. The retardation along a thickness direction(Rth), of the film is also preferably less than 100 nm, more preferablyless than 50 nm, further preferably less than 30 nm, furthermorepreferably less than 10 nm, and most preferably, less than 5 nm. The Reand Rth retardation values are defined by the following formula:

Re=(nx−ny)×d

Rth=[{(nx+ny)/2}−nz]×d

[0052] in which each of nx and ny is a refractive index in plane of thesupport; nz is a refractive index along the thickness direction of thesupport; and d is a thickness of the support.

[0053] According to the display mode of the liquid crystal cell, anoptically anisotropic polymer film may be used as the transparentsupport. In that case, the optical anisotropy of the liquid crystal cellis compensated with a combination of the optically anisotropic layer andthe optically anisotropic support, which is preferably opticallyuniaxial or biaxial. If the support is optically uniaxial, it may beeither optically positive (i.e., the refractive index along the opticalaxis is larger than that perpendicular to the optical axis) or opticallynegative (i.e., the refractive index along the optical axis is smallerthan that perpendicular to the optical axis). In an optically biaxialsupport, the refractive indexes of nx, ny and nz have different values.

[0054] The retardation in plane (Re) of the optically anisotropictransparent support is in the range of preferably 0 to 300 nm, morepreferably 0 to 200 nm, and most preferably 0 to 100 nm. The retardationalong the thickness direction (Rth) of the support is in the range ofpreferably 10 to 1,000 nm, more preferably 50 to 400 nm, and mostpreferably 100 to 300 nm.

[0055] The material of the support is determined according to whether itis optically isotropic or anisotropic. An optically isotropictransparent support is generally made of glass or cellulose esters,while an optically anisotropic support is made of synthetic polymers(e.g., polycarbonate, polysulfone, polyethersulfone, polyacrylate,polymethacrylate and norbornene resin). Further, a cellulose ester filmhaving high retardation (i.e., an optically-anisotropic cellulose esterfilm) can be obtained by the method described in European Patent No.0911656 A 2, in which the optically anisotropic cellulose ester film isprepared (1) with a retardation increasing agent (birefringenceincreasing agent), (2) by lowering the acetylation degree in thecellulose acetate film, or (3) through the cold dissolution process.

[0056] The transparent support of polymer film is preferably preparedaccording to a solvent casting method.

[0057] The polymer film is preferably stretched to prepare an opticallyanisotropic transparent support.

[0058] An optically uniaxial support can be obtained by normal uniaxialor biaxial stretching process.

[0059] An optically biaxial support is preferably produced by unbalancebiaxial stretching process, in which the polymer film is stretchedparallel to a certain direction to a predetermined extent (for example 3to 100%, preferably 5 to 30%) and stretched perpendicularly to moreextent (for example 6 to 200%, preferably 10 to 90%). The film may bestretched in the two directions at the same time.

[0060] It is preferred that the stretching direction (direction in whichthe film is stretched to the larger extent in unbalance biaxialstretching process) be essentially parallel to the slow axis in plane ofthe resulting film. The angle between them is preferably less than 10°,more preferably less than 5°, and most preferably less than 3°.

[0061] If the transparent support is optically uniaxial or biaxial, itis preferred that an average direction of lines obtained by projectingonto the support the optical axes of discotic liquid crystal moleculesin the optically isotropic layer be essentially parallel orperpendicular to the slow axis in plane of the support.

[0062] The transparent support has a thickness preferably in the rangeof 10 to 500 μm, and more preferably in the range of 50 to 200 μm.

[0063] The transparent support can be subjected to a surface treatment(e.g., glow discharge treatment, corona discharge treatment, ultraviolet(UV) treatment, flame treatment) to improve adhesion to a layer formedon the support (e.g., adhesive layer, orientation layer, opticallyanisotropic layer). An ultraviolet (UV) absorbing agent can beincorporated in the support.

[0064] An adhesive layer (undercoating layer) can be provided on thetransparent support. Japanese Patent Provisional Publication No.7(1995)-333433 describes an adhesive layer. The adhesive layer has athickness of preferably 0.1 to 2 μm, and more preferably 0.2 to 1 μm.

[0065] [Orientation Layer]

[0066] The orientation layer is preferably made of a copolymercomprising repeating units represented by the formula (I) and repeatingunits represented by the formula (II).

[0067] In the formula (I), R¹ is hydrogen, a halogen atom or an alkylgroup having 1 to 6 carbon atoms. R¹ is preferably hydrogen or an alkylgroup having 1 to 6 carbon atoms more preferably is hydrogen, methyl orethyl, and most preferably is hydrogen or methyl. In the case that R¹ ishydrogen, the copolymer is acrylic copolymer. In the case that R¹ ismethyl, the copolymer is methacrylic copolymer.

[0068] In the formula (I), M is an alkali metal ion (lithium ion, sodiumion, potassium ion, cesium ion).

[0069] Since the group of COOM is hydrophilic, the copolymer is solublein water. Accordingly, the orientation layer can be formed by using anaqueous medium.

[0070] In the formula (I), x is 10 to 95 mole %, and preferably is 25 to90 mole %.

[0071] In the formula (II), R² is hydrogen, a halogen atom or an alkylgroup having 1 to 6 carbon atoms. R² preferably is hydrogen or an alkylgroup having 1 to 6 carbon atoms, more preferably is hydrogen, methyl orethyl, and most preferably is hydrogen or methyl.

[0072] In the formula (II), L¹ is a divalent linking group selected fromthe group consisting of —O—, —CO—, —NH—, an alkylene group and acombination thereof. L¹ preferably is —CO—O—, —CO—NH—, —CO—O-alkylene-,—CO—O-alkylene-O— or —CO—O-alkylene-CO—O—, more preferably is —CO—O— or—CO—NH—.

[0073] The alkylene group can have a branched or cyclic structure. Thealkylene group contains preferably 1 to 30 carbon atoms, more preferably1 to 15 carbon atoms, and most preferably 1 to 12 carbon atoms.

[0074] In the formula (II), each of L², L³ and L⁴ is independently asingle bond or a divalent linking group selected from the groupconsisting of —O—, —CO—, —NH—, —SO₂—, an alkylene group, an alkenylenegroup, an alkynylene group and a combination thereof. At least one ofL², L³ and L⁴ preferably is a single bond or an alkynylene group, morepreferably is a single bond or ethynylene (—C≡C—), and most preferablyis ethynylene (—C≡C—). It is preferred that each of L², L³ and L⁴independently is a single bond, ethynylene, —CO—, —O—CO—, —CO—O—,-alkylene-O—, —CO—NH—, —O—CO—O—, —NH—SO₂— or —NH—CO—O—.

[0075] The alkylene group, the alkenylene group and the alkynylene groupcan have branched or cyclic structures. The alkylene group containspreferably 1 to 30 carbon atoms, more preferably 1 to 15 carbon atoms,and most preferably 1 to 12 carbon atoms. Each of the alkenylene groupand the alkynylene group contains preferably 2 to 30 carbon atoms, morepreferably 2 to 15 carbon atoms, and most preferably 2 to 12 carbonatoms.

[0076] In the formula (II), each of Ar¹, Ar², Ar³ and Ar⁴ independentlyis an aromatic ring (including an aromatic heterocyclic ring) which canhave a substituent group.

[0077] The aromatic ring preferably is a hydrocarbon aromatic ringhaving 6 to 18 carbon atoms. Examples of the hydrocarbon aromatic ringsinclude benzene ring, naphthalene ring, anthracene ring; phenanthrenering, pyrene ring and naphthacene ring. Each of Ar¹, Ar², Ar³ and Ar⁴more preferably is benzene ring or naphthalene ring, and most preferablyis benzene ring.

[0078] Examples of the substituent groups of the aromatic rings includea halogen atom, carboxyl, cyano, nitro, carbamoyl, sulfamoyl, an alkylgroup, an alkoxy group, an alkylthio group, an acyl group, an acyloxygroup, an alkylcarbamoyl group, an alkylsulfamoyl group, an amido group,a sulfonamido group and an alkylsulfonyl group.

[0079] The alkyl group can have a branched or cyclic structure. Thealkyl group contains preferably 1 to 20 carbon atoms, more preferably 1to 15 carbon atoms, further preferably 1 to 10 carbon atoms, and mostpreferably 1 to 6 carbon atoms.

[0080] In the formula (II), each of m and n is 0 or 1. It is preferredthat m be 0 or 1 and n be 0 (two or three aromatic rings). It is morepreferred that each of m and n be 0 (two aromatic rings).

[0081] In the formula (II), y is 5 to 90 mole %, preferably is 10 to 75mole %.

[0082] Examples of the repeating units represented by the formula (II)(except that L², L³ or L⁴ is —C≡C—) are shown below.

[0083] Examples of the (meth)acrylic copolymers (except that L², L³ orL⁴ is —C≡C—) are shown below. AA means a repeating unit derived fromacrylic acid (alkali metal salt), MA means a repeating unit derived frommethacrylic acid (alkali metal salt). The ratio of the repeating unitmeans mol %.

[0084] PA101: -(AA)60-(II-1)40-

[0085] PA102: -(AA)70-(II-2)30-

[0086] PA103: -(AA)60-(II-5)40-

[0087] PA104: -(AA)65-(II-9)35-

[0088] PA105: -(AA)70-(II-11)30-

[0089] PA106: -(AA)80-(II-15)20-

[0090] PA107: -(AA)70-(II-15)30-

[0091] PA108: -(AA)60-(II-15)40-

[0092] PA109: -(AA)70-(II-16)30-

[0093] PA110: -(AA)60-(II-16)40-

[0094] PA111: -(AA)50-(II-16)50-

[0095] PA112: -(AA)70-(II-18)30-

[0096] PA113: -(AA)60-(II-18)40-

[0097] PA114: -(AA)50-(II-18)50-

[0098] PA115: -(AA)60-(II-23)40-

[0099] PA116: -(AA)60-(II-25)40-

[0100] PA117: -(AA)60-(II-32)40-

[0101] PA118: -(AA)60-(II-35)40-

[0102] PA119: -(AA)60-(II-37)40-

[0103] PA120: -(AA)60-(II-45)40-

[0104] PA121: -(AA)60-(II-55)40-

[0105] PA122: -(MA)60-(II-1)40-

[0106] PA123: -(MA)70-(II-2)30-

[0107] PA124: -(MA)60-(II-5)40-

[0108] PA125: -(MA)65-(II-9)35-

[0109] PA126: -(MA)70-(II-11)30-

[0110] PA127: -(MA)80-(II-15)20-

[0111] PA128: -(MA)70-(II-15)30-

[0112] PA129: -(MA)60-(II-15)40-

[0113] PA130: -(MA)70-(II-16)30-

[0114] PA131: -(MA)60-(II-16)40-

[0115] PA132: -(MA)50-(II-16)50-

[0116] PA133: -(MA)70-(II-18)30-

[0117] PA134: -(MA)60-(II-18)40-

[0118] PA135: -(MA)60-(II-18)40-

[0119] PA136: -(MA)60-(II-23)40-

[0120] PA137: -(MA)60-(II-25)40-

[0121] PA138: -(MA)60-(II-32)40-

[0122] PA139: -(MA)60-(II-35)40-

[0123] PA140: -(MA)60-(II-37)40-

[0124] PA141: -(MA)60-(II-45)40-

[0125] PA142: -(MA)60-(II-55)40-

[0126] The side chain of the repeating unit preferably has a tolanstructure (wherein L², L³ or L⁴ is —C≡C—, and the rings attached to bothsides of —C≡C— are aromatic hydrocarbon rings).

[0127] Examples of the repeating unit having the side chain of a tolanstructure are shown below.

[0128] Examples of the (meth)acrylic copolymers comprising the repeatingunits having a tolan structure are shown below. AA means a repeatingunit derived from acrylic acid (alkali metal salt), and MA means arepeating unit derived from methacrylic acid (alkali metal salt). Theratio of the repeating unit means mol %.

[0129] PA201: -(AA)60-(II-101)40-

[0130] PA202: -(AA)70-(II-101)30-

[0131] PA203: -(AA)60-(II-102)40-

[0132] PA204: -(AA)65-(II-107)35-

[0133] PA205: -(AA)70-(II-111)30-

[0134] PA206: -(AA)80-(II-114)20-

[0135] PA207: -(AA)70-(II-120)30-

[0136] PA208: -(AA)60-(II-123)40-

[0137] PA209: -(AA)70-(II-125)30-

[0138] PA210: -(AA)60-(II-125)40-

[0139] PA211: -(AA)50-(II-125)50-

[0140] PA212: -(AA)70-(II-126)30-

[0141] PA213: -(AA)60-(II-128)40-

[0142] PA214: -(AA)50-(II-132)50-

[0143] PA215: -(AA)70-(II-133)30-

[0144] PA216: -(AA)60-(II-133)40-

[0145] PA217: -(AA)70-(II-138)30-

[0146] PA218: -(AA)60-(II-138)40-

[0147] PA219: -(AA)60-(II-139)40-

[0148] PA220: -(AA)60-(II-141)40-

[0149] PA221: -(AA)60-(II-143)40-

[0150] PA222: -(MA)60-(II-101)40-

[0151] PA223: -(MA)70-(II-101)30-

[0152] PA224: -(MA)60-(II-102)40-

[0153] PA225: -(MA)65-(II-107)35-

[0154] PA226: -(MA)70-(II-111)30-

[0155] PA227: -(MA)80-(II-114)20-

[0156] PA228: -(MA)70-(II-120)30-

[0157] PA229: -(MA)60-(II-123)40-

[0158] PA230: -(MA)70-(II-125)30-

[0159] PA231: -(MA)60-(II-125)40-

[0160] PA232: -(MA)50-(II-125)50-

[0161] PA233: -(MA)70-(II-126)30-

[0162] PA234: -(MA)60-(II-128)40-

[0163] PA235: -(MA)50-(II-132)50-

[0164] PA236: -(MA)70-(II-133)30-

[0165] PA237: -(MA)60-(II-133)40-

[0166] PA238: -(MA)70-(II-138)30-

[0167] PA239: -(MA)60-(II-138)40-

[0168] PA240: -(MA)60-(II-139)40-

[0169] PA241: -(MA)60-(II-141)40-

[0170] PA242: -(MA)60-(II-142)40-

[0171] PA243: -(MA)60-(II-143)40-

[0172] The (meth)acrylic copolymer can have a polymerizable group. Acopolymer having a polymerizable group is used in combination with adiscotic liquid crystal molecule having a polymerizable group tochemically bind the copolymer and the liquid crystal molecule along aninterface between an optically anisotropic layer and an orientationlayer. The mechanical strength of an optically anisotropic sheet usingdiscotic liquid crystal molecules can be improved by the chemical bond.

[0173] The polymerizable group of the (meth)acrylic copolymer isdetermined depending on the polymerizable group (Q) of the liquidcrystal molecule (described below). The polymerizable group (Q) of theliquid crystal molecule preferably is an unsaturated polymerizable group(Q1 to Q7 in the examples described about liquid crystal molecule), anepoxy group (Q8) or an aziridinyl group (Q), more preferably is anunsaturated polymerizable group, and most preferably is an ethylenicallyunsaturated group (Q1 to Q6). The polymerizable group of the(meth)acrylic copolymer is also preferably is an unsaturatedpolymerizable group, an aziridinyl group or an epoxy group, morepreferably is an unsaturated polymerizable group, and most preferably isan ethylenically unsaturated group.

[0174] The polymerizable group is preferably not directly attached tothe main chain of the (meth)acrylic copolymer. In other words, a linkinggroup preferably intervenes between the main chain and the polymerizablegroup. Examples of the linking groups include —CO—, —CO—O—, —CO—NH—,—CO—NH-alkylene-, —CO—NH-alkylene-O—, —CO—NH-alkylene-CO—O—,—CO—NH-alkylene-O—CO—, —CO—NH-alkylene-CO—NH—, —CO-alkylene-O—CO—,—CO-arylene-O-alkylene-O—CO—, —CO-arylene-O—alkylene-O—,—CO-arylene-O-alkylene- and —CO-alkylene-O—CO—, in which the left sideis attached to the main chain, and the right side is attached to thepolymerizable group.

[0175] The alkylene group can have a branched or cyclic structure. Thealkylene group contains preferably 1 to 30 carbon atoms, more preferably1 to 20 carbon atoms, further preferably 1 to 15 carbon atoms, and mostpreferably 1 to 12 carbon atoms.

[0176] The arylene group preferably is phenylene or naphthylene, morepreferably is phenylene, and most preferably is p-phenylene. The arylenegroup can have a substituent group. Examples of the substituent groupsinclude a halogen atom. (F, Cl, Br), carboxyl, cyano, nitro, carbamoyl,sulfamoyl, an alkyl group, a cycloalkyl group, an alkoxy group, analkylthio group, an acyl group, an acyloxy group, an alkylcarbamoylgroup, an alkylsulfamoyl group, an amido group, a sulfonamido group andan alkylsulfonyl group.

[0177] The alkyl group can have a branched structure. The alkyl grouppreferably contains 1 to 20 carbon atoms, more preferably contains 1 to15 carbon atoms, further preferably contains 1 to 10 carbon atoms, andmost preferably contains 1 to 6 carbon atoms.

[0178] The cycloalkyl group preferably is cyclohexyl.

[0179] The alkoxy group can have a branched structure. The alkoxy grouppreferably contains 1 to 20 carbon atoms, more preferably contains 1 to15 carbon atoms, further preferably contains 1 to 10 carbon atoms, andmost preferably contains 1 to 6 carbon atoms.

[0180] The alkylthio group can have a branched structure. The alkylthiogroup preferably contains 1 to 20 carbon atoms, more preferably contains1 to 15 carbon atoms, further preferably contains 1 to 10 carbon atoms,and most preferably contains 1 to 6 carbon atoms.

[0181] The acyl group preferably contains 2 to 20 carbon atoms, morepreferably contains 2 to 15 carbon atoms, further preferably contains 2to 10 carbon atoms, and most preferably contains 2 to 6 carbon atoms.

[0182] The acyloxy group preferably contains 2 to 20 carbon atoms, morepreferably contains 2 to 15 carbon atoms, further preferably contains 2to 10 carbon atoms, and most preferably contains 2 to 6 carbon atoms.

[0183] The alkylcarbamoyl group preferably contains 2 to 20 carbonatoms, more preferably contains 2 to 15 carbon atoms, further preferablycontains 2 to 10 carbon atoms, and most preferably contains 2 to 6carbon atoms. The alkyl moiety of the alkylcarbamoyl group can furtherhave a substituent group (e.g., an alkoxy group).

[0184] The alkylsulfamoyl group preferably contains 2 to 20 carbonatoms, more preferably contains 2 to 15 carbon atoms, further preferablycontains 2 to 10 carbon atoms, and most preferably contains 2 to 6carbon atoms. The alkyl moiety of the alkylsulfamoyl group can furtherhave a substituent group (e.g., an alkoxy group).

[0185] The amido group preferably contains 2 to 20 carbon atoms, morepreferably contains 2 to 15 carbon atoms, further preferably contains 2to 10 carbon atoms, and most preferably contains 2 to 6 carbon atoms.

[0186] The sulfonamido group preferably contains 1 to 20 carbon atoms,more preferably contains 1 to 15 carbon atoms, further preferablycontains 1 to 10 carbon atoms, and most preferably contains 1 to 6carbon atoms.

[0187] The alkylsulfonyl group preferably contains 1 to 20 carbon atoms,more preferably contains 1 to 15 carbon atoms, further preferablycontains 1 to 10 carbon atoms, and most preferably contains 1 to 6carbon atoms. The alkyl moiety of the alkylsulfonyl group can furtherhave a substituent group (e.g., an alkoxy group).

[0188] The side chain of the repeating unit can have two or morepolymerizable groups.

[0189] The polymerizable groups are introduced into the side chains ofrepeating units, or otherwise they are introduced into the repeatingunits represented by the formula (II).

[0190] The repeating unit having the polymerizable group at the sidechain is preferably represented by the formula (III).

[0191] In the formula (III), R³ is hydrogen or methyl.

[0192] In the formula (III), L¹¹ is a divalent linking group selectedfrom the group consisting of —NH-alkylene-O—CO—, -alkylene-O—CO—,—O-alkylene-O—CO—, —O-arylene-O-alkylene-O—CO—, —O-arylene-O-alkylene-,—O-arylene-O—, —NH-alkylene-O—CO—, —NH-alkylene-O— and —NH-alkylene. L¹¹preferably is —NH-alkylene-O—CO—, -alkylene-O—CO—, —O-alkylene-O—CO—,—O-arylene-O-alkylene-O—CO— or —NH-alkylene-O—CO—, and more preferablyis —NH-alkylene-O—CO—.

[0193] The alkylene group can have a branched or cyclic structure. Thealkylene group contains preferably 1 to 30 carbon atoms, more preferably1 to 20 carbon atoms, further preferably 1 to 15 carbon atoms, and mostpreferably 1 to 12 carbon atoms.

[0194] The arylene group preferably is phenylene or naphthylene, morepreferably is phenylene, and most preferably is p-phenylene. The arylenegroup can have a substituent group. Examples of the substituent groupsare the same as the above-described substituent groups.

[0195] In the formula (III), Q is a polymerizable group. Thepolymerizable group of the (meth)acrylic copolymer is preferablyanalogous to the polymerizable group (Q) of the liquid crystal molecule,as is described above.

[0196] Examples of the repeating units having a polymerizable group atthe side chain are shown below.

[0197] In the case that a repeating unit having a polymerizable group atthe side chain is introduced into a (meth)acrylic copolymer, thecopolymer preferably contains the polymerizable repeating units in anamount of 0.1 to 10 mol %, and more preferably in an amount of 3 to 5mol %.

[0198] The polymerizable group introduced into the repeating unitrepresented by the formula (II) is preferably a substituent group ofaromatic ring, more preferably a substituent group of aromatic ringpositioned at the end of the side chain.

[0199] The polymerizable group is preferably not directly attached tothe aromatic ring. In other words, a linking group preferably intervenesbetween the aromatic ring and the polymerizable group. Examples of thelinking groups include —O—, —CO—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NH,—SO₂—NH—, —NH—CO—, —NH—CO—O—, —NH—S₂—, -alkylene-, -alkenylene-,-alkynylene-, —O-alkylene- and -alkylene-O—, in which the left side isattached to the aromatic ring, and the right side is attached to thepolymerizable group.

[0200] The alkylene group can have a branched or cyclic structure. Thealkylene group contains preferably 1 to 30 carbon atoms, more preferably1 to 20 carbon atoms, further preferably 1 to 15 carbon atoms, and mostpreferably 1 to 12 carbon atoms.

[0201] The alkenylene group can have a branched or cyclic structure. Thealkenylene group contains preferably 2 to 30 carbon atoms, morepreferably 2 to 20,carbon atoms, further preferably 2 to 15 carbonatoms, and most preferably to 12 carbon atoms.

[0202] The alkynylene group can have a branched or cyclic structure. Thealkynylene group contains preferably 2 to 30 carbon atoms, morepreferably 2 to 20 carbon atoms, further preferably 2 to 15 carbonatoms, and most preferably 2 to 12 carbon atoms.

[0203] The aromatic ring (including aromatic heterocyclic ring) can havetwo or more polymerizable groups.

[0204] A repeating unit obtained by introducing the polymerizable groupto the repeating unit represented by the formula (II) is preferablyrepresented by the formula (IV).

[0205] In the formula (IV), R⁵ is hydrogen or methyl.

[0206] In the formula (IV), L²¹ is a single bond or a divalent linkinggroup selected from the group consisting of —CO—, —CO—NH—, -alkylene-,—CO—NH-alkylene-, —CO—NH-alkylene-O—, —CO—NH-alkylene-CO—O— and—CO—NH-alkylene-CO—NH—, preferably is —CO—, —CO—NH— or -alkylene, andmore preferably is —CO—NH—.

[0207] The alkylene group can have a branched or cyclic structure. Thealkylene group contains preferably 1 to 30 carbon atoms, more preferably1 to 20 carbon atoms, further preferably 1 to 15 carbon atoms, and mostpreferably 1 to 12 carbon atoms.

[0208] In the formula (IV), each of L²², L²³, L²⁴and L²⁵ independentlyis a single bond, —O—, —CO—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NH—,—SO₂—NH—, —NH—CO—, —NH—CO—O—, —NH—SO₂—, -alkylene-, -alkenylene-,-alkynylene-, —O-alkylene- or -alkylene-O—. At least one of L²², L²³ andL²⁴ preferably is a single bond or -alkynylene-.

[0209] In the formula (IV), each of Ar²¹, Ar²², Ar²³ and Ar²⁴independently is an aromatic ring (including an aromatic heterocyclicring), and preferably is benzene ring. Each of Ar²¹, Ar²² and Ar²³preferably is p-phenylene. The aromatic ring can have a substituentgroup. Examples of the substituent groups are the same as the examplesof the substituent groups of the aromatic ring in the formula (VI).

[0210] In the formula (IV), each of q and r is 0 or 1. It is preferredthat q be 0 or 1 and r be 0 (two or three aromatic rings). It is morepreferred that each of q and r be 0 (two aromatic rings).

[0211] In the formula (IV), p is 1, 2, or 3, preferably is 1 or 2, andmore preferably is 1.

[0212] Examples of the repeating units having the polymerizable groupand two or more aromatic rings at the side chain are shown below.

[0213] The orientation layer has a thickness preferably in the range of0.01 to 10 μm, more preferably in the range of 0.05 to 5 μm, and mostpreferably in the range of 0.1 to 1 μm.

[0214] After aligning discotic liquid crystal molecules in an opticallyanisotropic layer, the formed layer can be transferred onto atransparent support. Since the liquid crystal molecules are fixed, thealignment can be kept without the orientation layer.

[0215] The orientation layer is preferably formed by a process, whichcomprises the steps of: coating a solution of the (meth)acryliccopolymer on a support to form a coated layer; drying the coated layer;rubbing a surface of the coated layer; and heating the coated layer.

[0216] The coated layer is heated preferably at 50 to 300° C., morepreferably at 50 to 250° C., and most preferably at 100 to 250°C.

[0217] The coated layer can be heated by, for example, attaching thelayer on the support to a surface of a heating medium, placing the layeron the support in a heated vessel, or splaying a hated gas (preferably,air) to the layer on the support along a rubbing direction. The heatingmedium preferably is a plate. The heating time depends on the heatingtemperature. Where the heating temperature is 100° C., the heating timeis preferably in the range of 1 to 30 minutes. Where the heatingtemperature, is 130° C., the heating time is preferably in the range of30 seconds to 10 minutes. Where the heating temperature is 160° C., theheating time is preferably in the range of 10 seconds to 3 minutes. Theinterval between the rubbing treatment and the heating treatment ispreferably not longer than 1 week, more preferably not longer than 3days, and most preferably not longer than 3 hours.

[0218] [Optically Anisotropic Layer]

[0219] The optically anisotropic layer comprises discotic liquid crystalmolecules, which are aligned by the above-described orientation layer sothat their discotic planes are arranged essentially vertically (at theaverage inclined angle of 50 to 90°) to the orientation layer. Thediscotic liquid crystal molecules are preferably fixed in the opticallyanisotropic layer with their vertical (homogeneous) alignmentmaintained. The discotic liquid crystal molecules are preferably fixedby a polymerization reaction.

[0220] The discotic liquid crystal molecule is described in variousdocuments (C. Destrade et al, Mol. Crysr. Liq. Cryst., vol. 71, page 111(1981); Japan Chemical Society, Quarterly Chemical Review (written inJapanese), chapter 5 and chapter 10, section 2 (1994); B. Kohne et al.,Angew. Chem. Soc. Chem. Comm., page 1794 (1985); and J. Zhang et al., J.Am. Chem. Soc., vol. 116, page 2655 (1994)). The polymerization reactionof the discotic liquid crystal molecule is described in Japanese PatentProvisional Publication No. 8(1996)-27284.

[0221] A polymerizable group should be bound to a discotic core of thediscotic liquid crystal molecule to cause the polymerization reaction ofthe compound. However, if the polymerizable group is directly bound tothe discotic core, it is difficult to keep the alignment at thepolymerization reaction. Therefore, a linking group is introducedbetween the discotic core and the polymerizable group. Accordingly, thediscotic liquid crystal molecule having a polymerizable group(polymerizable discotic liquid crystal molecule) preferably is acompound represented by the following formula.

D(-L-Q)_(n)

[0222] in which D is a discotic core; L is a divalent linking group; Qis a polymerizable group; and n is an integer of 4 to 12.

[0223] Examples of the discotic cores (D) are shown below. In theexamples, LQ (or QL) means the combination of the divalent linking group(L) and the polymerizable group (Q).

[0224] In the formula, the divalent linking group (L) preferably isselected from the group consisting of an alkylene group, an alkenylenegroup, an arylene group, —CO, —NH—, —O—, —S— and combinations thereof. Lmore preferably is a divalent linking group comprising at least twodivalent groups selected from the group consisting of an alkylene group,an alkenylene group, an arylene group, —CO—, —NH—, —O— and —S—. L mostpreferably is a divalent linking group comprising at least two divalentgroups selected from the group consisting of an alkylene group, analkenylene group, an arylene group, —CO— and —O—. The alkylene grouppreferably has 1 to 12 carbon atoms. The alkenylene group preferably has2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbonatoms. The alkylene group, the alkenylene group and the arylene groupcan have a substituent group (such as an alkyl group, a halogen atom,cyano, an alkoxy group, an acyloxy group).

[0225] Examples of the divalent linking groups (L) are shown below. Inthe examples, the left side is attached to the discotic core (D), andthe right side is attached to the polymerizable group (Q). The AL meansan alkylene group or an alkenylene group. The AR means an arylene group.

[0226] L1: -AL-CO—O-AL-

[0227] L2: -AL-CO—O-AL-O—

[0228] L3: -AL-CO—O-AL-O-AL-

[0229] L4: -AL-CO—O-AL-O—CO—

[0230] L5: —CO-AR—O-AL-

[0231] L6: —CO-AR—O-AL-O—

[0232] L7: —CO-AR—O-AL-O—CO—

[0233] L8: —CO—NH-AL-

[0234] L9: —NH-AL-O—

[0235] L10: —NH-AL-O—CO—

[0236] L11: —O-AL-

[0237] L12: —O-AL-O—

[0238] L13: —O-AL-O—CO—

[0239] L14: —O-AL-O—CO—NH-AL-

[0240] L15: —O-AL-S-AL-

[0241] L16: —O—CO-AL-AR—O-AL-O—CO—

[0242] L17: —O—CO-AR—O-AL-CO—

[0243] L18: —O—CO-AR—O-AL-O—CO—

[0244] L19: —O—CO-AR—O-AL-O-AL-O—CO—

[0245] L20: —O—CO-AR—O-AL-O-AL-O-AL-O—CO—

[0246] L21: —S-AL-

[0247] L22: —S-AL-O—

[0248] L23: —S-AL-O—CO—

[0249] L24: —S-AL-S-AL-

[0250] L25: —S-AR-AL-

[0251] The polymerizable group (Q) is determined by the polymerizationreaction. Examples of the polymerizable groups (Q) are shown below.

[0252] The polymerizable group (Q) preferably is an unsaturatedpolymerizable group (Q1 to Q7), an epoxy group (Q8) or an aziridinylgroup (Q9), more preferably is an unsaturated polymerizable group, andmost preferably is an ethylenically unsaturated group (Q1 to Q6).

[0253] In the formula, n is an integer of 4 to 12, which is determinedby the chemical structure of the discotic core (D). The 4 to 12combinations of L and Q can be different from each other. However, thecombinations are preferably identical.

[0254] Two or more discotic liquid crystal molecules can be used incombination. For example, a molecule having a polymerizable group (Q)can be used in combination with a molecule having no polymerizable group(non-polymerizable discotic liquid crystal molecule).

[0255] The discotic liquid crystal molecule having no polymerizablegroup (non-polymerizable discotic liquid crystal molecule) is obtainedby replacing the polymerizable group (Q) of the above-describedpolymerizable discotic liquid crystal molecule with hydrogen or an alkylgroup. Accordingly, the discotic liquid crystal molecule having nopolymerizable group preferably is a compound represented by thefollowing formula.

D(-L-R)_(n)

[0256] in which D is a discotic core; L is a divalent linking group; Ris hydrogen or an alkyl group; and n is an integer of 4 to 12.

[0257] Examples of the discotic cores are the same as the examples ofthe cores in the polymerizable discotic liquid crystal molecule, exceptthat LQ or QL is replaced with LR or RL, respectively.

[0258] Examples of the divalent linking groups are also the same as theexamples of the linking groups in the polymerizable discotic liquidcrystal molecule.

[0259] The alkyl group of R contains preferably 1 to 40 carbon atoms,and more preferably 1to 30 carbon atoms. An alkyl group preferably has achain structure rather than a cyclic structure. An alkyl group having astraight chain (normal alkyl group) is preferred to a branched alkylgroup. R particularly preferably is hydrogen or a normal alkyl grouphaving 1 to 30 carbon atoms.

[0260] The optically anisotropic layer can contain a fluorine-containingsurface active agent or a cellulose ester, which has a function ofuniformly and essentially vertically (homogeneously) aligning discoticliquid crystal molecules placed near an interface between the layer andthe air.

[0261] The fluorine-containing surface active agent comprises ahydrophobic group containing fluorine, a nonionic, anionic, cationic oramphoteric hydrophilic group and an optional linking group.

[0262] The fluorine-containing surface active agent may have two or morehydrophobic groups containing fluorine or two or more hydrophilicgroups. Two or more fluorine-containing surface active agents can beused in combination.

[0263] The surface active agents are described in various documents,such as Hiroshi Horiguchi, New Surface Active Agents, Sankyo Shuppan,1975 (written in Japanese), M. J. Schick, Nonionic Surfactants, MarcellDekker Inc., New York, 1967 and Japanese Patent Provisional PublicationNo. 7(1995)-13293.

[0264] The fluorine-containing surface active agent is used in an amountof 0.01 to 30 wt. % based on the amount of the discotic liquid crystalmolecules. The amount is preferably in the range of 0.05 to 10 wt. %,and more preferably in the range of 0.1 to 5 wt. %.

[0265] The cellulose ester preferably is a cellulose ester of a lowerfatty acid.

[0266] The term “lower fatty acid” of the cellulose ester means a fattyacid having 1 to 6 carbon atoms. The lower fatty acid preferably has 2to 5 carbon atoms, and more preferably has 2 to 4 carbon atoms. Thefatty acid may have a substituent group (e.g., hydroxyl). Two or morefatty acids may form an ester with cellulose acetate.

[0267] The coating amount of the cellulose ester is preferably in therange of 0.005 to 0.5 g/m², more preferably in the range of 0.01 to 0.45g/m², further preferably in the range of 0.02 to 0.4 g/m², and mostpreferably in the range of 0.03 to 0.35 g/m². The amount of thecellulose ester is also preferably in the range of 0.1 to 5 wt. % basedon the amount of the discotic liquid crystal molecule.

[0268] An optically anisotropic layer can be formed by coating on anorientation layer a solution containing the discotic liquid crystalmolecules and, if needed, the above-mentioned additive (afluorine-containing surface-active agent, a cellulose ester), and apolymerization initiator (described below).

[0269] A solvent for the preparation of the solution preferably is anorganic solvent. Examples of the organic solvents include amides (e.g.,dimethylformamide), sulfoxides (e.g., dimethylsulfoxide), heterocycliccompounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), alkylhalides (e.g., chloroform, dichloromethane), esters (e.g., methylacetate, butyl acetate), ketones (e.g., acetone, methyl ethyl ketone)and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halidesand ketones are preferred. Two or more organic solvents can be used incombination.

[0270] The solution can be coated according to a conventional coatingmethod such as an extrusion coating method, a direct gravure coatingmethod, a reverse gravure coating method, a die coating method or a barcoating method.

[0271] The aligned discotic liquid crystal molecules are fixed whilekeeping their essentially vertical (homogeneous) alignment. The discoticliquid crystal molecules are fixed preferably by a polymerizationreaction of the polymerizable groups (Q) in the molecules. Thepolymerization reaction can be classified a thermal reaction using athermal polymerization initiator and a photo reaction using a photopolymerization initiator. A photo polymerization reaction is preferred.

[0272] Examples of the photo polymerization initiators includeα-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661, 2,367,670),acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbonsubstituted acyloin compounds (described in U.S. Pat. No. 2,722,512),poly-cyclic quinone compounds (described in U.S. Pat. Nos. 2,951,758,3,046,127), combinations of triarylimidazoles and p-aminophenyl ketones(described in U.S. Pat. No. 3,549,367), acridine or phenazine compounds(described in Japanese Patent Provisional Publication No.60(1985)-105667 and U.S. Pat. No. 4,239,850) and oxadiazole compounds(described in U.S. Pat. No. 4,212,970).

[0273] The amount of the photo polymerization initiator is preferably inthe range of 0.01 to 20 wt. %, and more preferably in the range of 0.5to 5 wt. % based on the solid content of the coating solution of thelayer.

[0274] The light irradiation for the photo polymerization is preferablyconducted by an ultraviolet ray.

[0275] The exposure energy is preferably in the range of 20 to 50,000 mJper cm², and more preferably in the range of 100 to 2,000 mJ per cm².The light irradiation can be conducted while heating the layer toaccelerate the photo polymerization reaction.

[0276] The optically anisotropic layer has a thickness preferably in therange of 0.1 to 50 μm, more preferably 1 to 30 μm, and most preferablyin the range of 5 to 20 μm. In the case that two optical compensatorysheets are used in a liquid crystal display, the preferred thickness ofthe layer is half of the preferred thickness (described above) in thecase that one optical compensatory sheet is used in a liquid crystaldisplay.

[0277] The discotic liquid crystal molecules in the opticallyanisotropic layer are aligned at an average inclined angle in the rangeof 50° to 90°. The inclined angle is preferably uniform. However, theinclined angle can be changed if the angle is continuously changed alongthe thickness of the optical anisotropic layer.

[0278] The words “optical axes of the discotic liquid crystal moleculesare parallel to the rubbing direction of the orientation layer” meanthat those of the liquid crystal molecules near the orientation layerare parallel to the rubbing direction. Accordingly, as long as theliquid crystal molecules near the orientation layer are thus arranged,the molecules may be oriented slightly in twisted alignment from theorientation layer to the air.

[0279] The total retardation of optically anisotropic sheet ispreferably adjusted by the optically anisotropic layer. A totalretardation in plane (Re) of the optically anisotropic sheet is in therange of preferably 20 to 200 nm, more preferably 20 to 100 nm, and mostpreferably 20 to 70 nm. A total retardation along the thicknessdirection (Rth) of the optically anisotropic sheet is in the range ofpreferably 70 to 500 nm, more preferably 70 to 400 nm, and mostpreferably 70 to 300 nm. The Re and Rth retardation values are definedby the following formulas.

Re=(nx−ny)×d

Rth=[{(nx+ny)/2}−nz]×d

[0280] in which each of nx and ny is a refractive index in plane of theoptically anisotropic sheet; nz is a refractive index along thethickness direction of the optically anisotropic sheet; and d is athickness of the optically anisotropic sheet.

[0281] The total retardation of optically anisotropic sheet can beadjusted by combination of the optically anisotropic layer and theoptically uniaxial or biaxial transparent support.

[0282] [Polarizing Film]

[0283] The polarizing film is an iodine polarizing film, a dyepolarizing film comprising a dichromatic dye or a polyene polarizingfilm. The iodine polarizing film and the dye polarizing film aregenerally prepared from polyvinyl alcohol films. The transparent axis ofthe film is perpendicular to the stretched direction.

[0284] The polarizing film is placed so that the transparent axis may beessentially perpendicular to an average direction of lines obtained byprojecting the optical axes of discotic liquid crystal molecules ontothe support.

[0285] [Transparent Protective Film]

[0286] As the transparent protective film, a polymer film is used. Here,‘transparent’ means that the film has an optical transmittance of notless than 80%.

[0287] The film is generally a cellulose ester film, preferably atriacetylcellulose film, which is preferably prepared according to thesolvent casting method.

[0288] The thickness of the film is within preferably 20 to 500 μm, morepreferably 50 to 200 μm.

[0289] [Liquid Crystal Display]

[0290] The present invention can be applied to liquid crystal displaysof various modes. As described above, the optical compensatory sheetsfor liquid crystal cells of various modes have been proposed. Examplesof the modes include TN (twisted nematic) mode, IPS (in-plane switching)mode, FLC (ferroelectric liquid crystal) mode, OCB (opticallycompensatory bend) mode, STN (super twisted nematic) mode, VA(vertically aligned) mode, ECB (electrically controlled birefringence)mode and HAN (hybrid aligned nematic) mode.

[0291] The optically anisotropic sheet of the invention are preferablyused in a liquid crystal display in which the optical axes of discoticliquid crystal molecules are essentially perpendicular to thetransparent axis of the polarizing film (i.e., the slow axis of thecompensatory sheet is preferably essentially parallel to the transparentaxis of the polarizing film), such as a liquid crystal display of TN orVA mode. The invention is particularly effective in a liquid crystaldisplay of VA mode.

[0292] The liquid crystal cell of VA mode include: (1) a liquid crystalcell of VA-mode in a narrow sense (described in Japanese PatentProvisional Publication No. 2(1990)-176625), in which rod-like liquidcrystal molecules are essentially vertically aligned while voltage isnot applied, and the molecules are essentially horizontally alignedwhile voltage is applied; (2) a liquid crystal cell of MVA mode(described in SID97, Digest of tech. Papers, 28(1997), 845), in whichthe VA mode is modified to be multi-domain type to enlarge the viewingangle; (3) a liquid crystal cell of n-ASM mode (described in NipponEkisho Toronkai [Liquid crystal forum of Japan], Digest of tech. Papers(1998), 58-59), in which rod-like liquid crystal molecules areessentially vertically aligned while voltage is not applied, and themolecules are essentially oriented in twisted multi-domain alignmentwhile voltage is applied; and (4) a liquid crystal cell of SURVAIVALmode (published in LCD international 98).

REFERENCE EXAMPLE 1

[0293] (Preparation of Optically Anisotropic Sheet)

[0294] The acrylic copolymer (PA210X) with triethylamine (counter ion,neutralizing agent) was dissolved in a mixture of methanol and water(volume ratio: 30/70) to prepare a 4 wt. % solution.

[0295] The solution was coated on the glass plate by means of a barcoater (thickness: 1 μm), and air-dried at 120° C. for 5 minutes. Thesurface was subjected to a rubbing treatment to form an orientationlayer. The following coating solution was then coated on the orientationlayer by means of a bar coater (thickness: 2 μm). Coating solution foroptically anisotropic layer The following discotic liquid crystalcompound (1) 100 weight parts Trimethylolpropane triacrylate denaturedwith ethylene  10 weight parts oxide (V#360, Osaka Organic ChemicalsCo., Ltd.) A photopolymerization initiator (Irgacure 369, Ciba-  3weight parts Geigy) Methyl ethyl ketone 400 weight parts Discotic liquidcrystal compound (1)

[0296] The coated layer was heated at 150° C. for 2 minutes toessentially vertically align the discotic liquid crystal molecules. Atthe heated temperature, the layer was irradiated with an ultraviolet rayfor 4 seconds to polymerize the liquid crystal molecules and to fix thealignment.

[0297] The alignment and the director (average optical axes, namely,average direction of normal lines to the discotic planes) of thediscotic liquid crystal molecules in the thus-prepared sheet wereobserved with a polarizing microscope. As a result, the director wasperpendicular to the rubbing direction. The retardation in plane (Re)was also measured with an ellipsometer, and from the obtained angledependence an average inclined angle was determined 89°.

REFERENCE EXAMPLES 2 to 15

[0298] (Preparation of Optically Anisotropic Sheet)

[0299] The procedure of Reference Example 1 was repeated except that thecopolymer, the counter ion (neutralizing agent) and the discotic liquidcrystal compound were changed as shown in Table 1, to prepare opticallyanisotropic sheets. In the Table 1, “X” and “Y” marked at the copolymersmean the counter ions (neutralizing agents) of triethylamine andammonia, respectively.

[0300] The alignment and the director (average optical axes, namely,average direction of normal lines to the discotic planes) of thediscotic liquid crystal molecules in each thus-prepared sheet wereobserved with a polarizing microscope. As a result, each director wasperpendicular to the rubbing direction. The retardation in plane (Re)was also measured with an ellipsometer, and from the obtained angledependence an average inclined angle was determined. The results are setforth in Table 1. TABLE 1 Optically Discotic anisotropic liquid sheetCopolymer crystal Incline angle Ref. Ex. 1 PA210X (1) 89° Ref. Ex. 2PA210X (4) 89° Ref. Ex. 3 PA210Y (1) 89° Ref. Ex. 4 PA216X (1) 89° Ref.Ex. 5 PA216X (4) 89° Ref. Ex. 6 PA216Y (4) 89° Ref. Ex. 7 PA242X (1) 89°Ref. Ex. 8 PA242X (2) 89° Ref. Ex. 9 PA242X (3) 89° Ref. Ex. 10 PA242X(4) 89° Ref. Ex. 11 PA242Y (1) 89° Ref. Ex. 12 PA242Y (4) 89° Ref. Ex.13 PA243X (1) 89° Ref. Ex. 14 PA243X (4) 89° Ref. Ex. 15 PA243Y (4) 89°PA210Y

PA216X

PA216Y

PA242X

PA242Y

PA243X

PA243Y

Discotic liquid crystal compound (2)

Discotic liquid crystal compound (3)

Discotic liquid crystal compound (4)

EXAMPLES 1 to 28

[0301] (Preparation of Optically Anisotropic Sheet)

[0302] The procedure of Reference Example 1 was repeated except that thecopolymer, the counter ion (neutralizing agent) and the discotic liquidcrystal compound were changed as shown in Table 2, to prepare opticallyanisotropic sheets. In the Table 2, the mark Na, K, Li or Cs attached tothe copolymer means that the counter ion (neutralizing agent) is sodiumion (sodium hydroxide), potassium ion (potassium hydroxide), lithium ion(lithium hydroxide) or cesium ion (cesium hydroxide).

[0303] The alignment and the director (average optical axes, namely,average direction of normal lines to the discotic planes) of thediscotic liquid crystal molecules in each of the prepared sheets wereobserved with a polarizing microscope. As a result, each director wasparallel to the rubbing direction. The retardation in plane (Re) wasalso measured with an ellipsometer, and from the obtained angledependence an average inclined angle was determined. The results are setforth in Table 2. TABLE 2 Optically Discotic anisotropic liquid sheetCopolymer crystal Incline angle Example 1 PA210Na (1) 89° Example 2PA210Na (2) 89° Example 3 PA210Na (3) 90° Example 4 PA210Na (4) 90°Example 5 PA210K (4) 90° Example 6 PA210Li (4) 90° Example 7 PA210Cs (4)90° Example 8 PA216Na (1) 89° Example 9 PA216Na (2) 89° Example 10PA216Na (3) 90° Example 11 PA216Na (4) 90° Example 12 PA216K (4) 90°Example 13 PA216Li (4) 90° Example 14 PA216Cs (4) 90° Example 15 PA242Na(1) 89° Example 16 PA242Na (2) 89° Example 17 PA242Na (3) 90° Example 18PA242Na (4) 90° Example 19 PA242K (4) 90° Example 20 PA242Li (4) 90°Example 21 PA242Cs (4) 90° Example 22 PA243Na (1) 89° Example 23 PA243Na(2) 89° Example 24 PA243Na (3) 90° Example 25 PA243Na (4) 90° Example 26PA243K (4) 90° Example 27 PA243Li (4) 90° Example 28 PA243Cs (4) 90°

EXAMPLE 29

[0304] (Preparation of Polarizing Plate)

[0305] A rolled polyvinyl alcohol film (thickness: 80 μm) wascontinuously stretched to the extent of five times length in an aqueoussolution of iodine, and dried to form a polarizing film. A rolledsaponified cellulose triacetate film (Fuji Tac TD80UF, Fuji Photo FilmCo., Ltd.) was laminated on one surface of the polarizing film. On theother surface, a saponified rolled optically anisotropic sheet preparedin Example 1 was so laminated that the optically anisotropic layer ofthe sheet is in contact with the polarizing film. Thus, a polarizingplate was prepared. The slow axis of the compensatory sheet (directionof the discotic planes of the discotic liquid crystal molecules) wasparallel to the transparent axis of the polarizing film. In other words,the optical axes of the discotic liquid crystal molecules wereperpendicular to the transparent axis of the polarizing film.

What is claimed is:
 1. An optically anisotropic sheet comprising anoptically anisotropic layer formed from discotic liquid crystalmolecules, an orientation layer subjected to rubbing treatment and atransparent support in this order, wherein the discotic liquid crystalmolecules are so aligned that an average inclined angle of discoticplanes of the discotic liquid crystal molecules is in the range of 50°to 90° and that an average direction of the discotic planes of thediscotic liquid crystal molecules is essentially perpendicular to arubbing direction of the orientation layer.
 2. The optically anisotropicsheet as defined in claim 1, wherein the support has an oblong shape,and the average direction of the discotic planes of the discotic liquidcrystal molecules is essentially parallel to a longitudinal direction ofthe support.
 3. The optically anisotropic sheet as defined in claim 1,wherein the support has an oblong shape, and the rubbing direction ofthe orientation layer is essentially parallel to a longitudinaldirection of the support.
 4. A rolled polarizing plate comprising anoptically anisotropic layer formed from discotic liquid crystalmolecules, an orientation layer subjected to rubbing treatment, atransparent support, a polarizing film and a transparent protective filmin this order, wherein the discotic liquid crystal molecules are soaligned that an average inclined angle of discotic planes of thediscotic liquid crystal molecules is in the range of 50° to 90° and thatan average direction of the discotic planes of the discotic liquidcrystal molecules is essentially perpendicular to a rubbing direction ofthe orientation layer.
 5. The polarizing plate as defined in claim 4,wherein the average direction of the discotic planes of the discoticliquid crystal molecules is essentially perpendicular to a longitudinaldirection of the plate.
 6. The polarizing plate as defined in claim 4,wherein the rubbing direction of the orientation layer is essentiallyparallel to a longitudinal direction of the plate.
 7. The polarizingplate as defined in claim 4, wherein the transparent axis of thepolarizing film is essentially perpendicular to a longitudinal directionof the plate.